I. Field
The present disclosure relates generally to communication, and more specifically to techniques for maintaining call continuity in wireless communication.
II. Background
Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, etc. These networks may be multiple-access networks capable of supporting communication for multiple users by sharing the available network resources. Examples of such multiple-access networks include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.
A CDMA network may implement a radio access technology (RAT) such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes Wideband-CDMA (W-CDMA) and Low Chip Rate (LCR). cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA network may implement a RAT such as Global System for Mobile Communications (GSM). These various RATs and standards are known in the art. UTRA and GSM are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). cdma2000 is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). 3GPP and 3GPP2 documents are publicly available.
Different RATs typically have different capabilities, and different releases of a given RAT may also have different capabilities. For example, GSM is a second-generation (2G) RAT that supports voice and low rate data services. W-CDMA is a third-generation (3G) RAT that supports concurrent voice and data services, higher data rates, and other enhanced features. Each RAT may support circuit-switched (CS) and/or packet-switched (PS) calls. Circuit-switched refers to transfer of data for a user via dedicated resources (e.g., a dedicated traffic channel) assigned to the user. Packet-switched refers to transfer of data for a user via common resources (e.g., a shared traffic channel) that may be shared by multiple users.
A user equipment (UE) may be capable of communicating with wireless networks of different RATs such as W-CDMA and GSM. This capability may allow a user to obtain the performance advantages of W-CDMA and the coverage benefits of GSM with the same UE. The UE may have a voice call with one wireless network and may roam throughout the network or to another wireless network. It is desirable for the UE to maintain the voice call even as the user roams about.
There is therefore a need in the art for techniques to maintain call continuity in wireless communication.